Amine neurotransmitters and their metabolites are studied in blood, cerebrospinal fluid (CSF), and urine to assess neurochemical alterations which may be associated with clinical diagnoses, clinical states, particular behavioral or psychopathological dimensions, or treatment with drugs. A high pressure liquid chromatographic assay for monoamine neurotransmitters and their metabolites in blood, urine, and CSF was developed. Two further studies confirm previous reports of an association between low CSF 5-hydroxyindoleacetic acid and impulse dyscontrol, extending this finding to psychopathic murderers and to suicidal individuals with schizophrenia. In studies of urinary metabolites, five different antidepressant treatments, including lithium and electroconvulsive therapy, have been shown to reduce total norepinephrine turnover. Urinary phenylethylamine excretion was elevated in rapid-cycling bipolar patients during delusional episodes.